1. Field of the Invention
The present invention relates to a method for measuring strength of an image forming surface of a planographic printing plate, a planographic printing plate and a packaging structure for planographic printing plates.
2. Description of the Related Art
Planographic printing plates, such as photosensitive and heat-sensitive printing plates, have been widely used in plate-making methods (including xerographic plate-making methods) of recent years to facilitate automation of plate-making processes. Planographic printing plates are generally manufactured in the following manner. Surface treatments such as graining, anodizing, silicate treatment and other chemical conversion treatments are administered, alone or in combination, to a support comprising, for example, a sheet-shaped or coiled aluminum plate. Thereafter, a photosensitive or heat-sensitive layer (hereinafter, these layers will be collectively referred to as xe2x80x9capplied filmsxe2x80x9d, a surface of a support on which an applied film has been applied will be referred to as an xe2x80x9cimage forming surfacexe2x80x9d, and a surface of a support on which an applied film has not been applied will be referred to as a xe2x80x9cnon-image forming surfacexe2x80x9d) is applied onto the support and dried, and then the support having the layer applied thereon is cut to a desired size.
The planographic printing plate is subjected to plate-making processings such as exposure, development, gum coating and the like, set into a printer and applied with ink, whereby characters, images or the like are printed on paper.
Sometimes the planographic printing plates are stacked in a thickness direction to form a stacked sheaf so that the planographic printing plates may be handled with greater efficiency. In this case, it is preferable to protect the image forming surfaces (i.e., applied films) of the planographic printing plates by, for example, contacting the image forming surfaces with papers known as xe2x80x9cinterleaf sheetsxe2x80x9d and stacking the planographic printing plates so that an interleaf sheet is disposed between each of the planographic printing plates.
Further, there are also cases in which, depending on the type of image forming surface, the image forming surfaces of the planographic printing plates have enough strength to withstand the kinds of damage that present problems in actual use when the planographic printing plates are packaged (or stacked) without interleaf sheets.
However, no quantitative standards or indices for such strengths of image forming surfaces have been proposed.
Also, when planographic printing plates to which interleaf sheets have been contacted to the image forming surfaces of the planographic printing plates are used in automatic plate-making machines, it is necessary to peel the interleaf sheets from the planographic printing plates. Consequently, efficiency of the plate-making operation can be improved when a so-called plate setter or an automatic plate-making machine having an automatic plate-feed function that automatically peels the interleaf sheets from the planographic printing plates and feeds the planographic printing plates is used.
However, when planographic printing plates and interleaf sheets are alternately stacked in a thickness direction to form a stacked sheaf, surfaces (non-contact surfaces) of the interleaf sheets opposite the surfaces that contact the image forming surfaces of the planographic printing plates come into contact with surfaces of the planographic printing plates (an image forming surface in the case of a planographic printing plate having image forming surfaces on both sides thereof, and a non-image forming surface in the case of a planographic printing plate having only one image forming surface) adjacent to the non-contact surfaces of the interleaf sheets. When the non-contact surfaces of the interleaf sheets strongly adhere to these surfaces of the planographic printing plates, the planographic printing plates are supplied without the interleaf sheets having been peeled therefrom, whereby drawbacks sometimes arise such as the automatic plate-feed operation stopping. For example, when a planographic printing plate is raised by the image forming surface thereof being adsorbed, the interleaf sheet protecting the image forming surface of the adjacent planographic printing plate also adheres to the surface of the opposite side of the planographic printing plate and is raised, resulting in both the planographic printing plate and the interleaf sheet being integrally supplied. Further, when the planographic printing plate is raised by the non-image forming surface thereof being adsorbed, there is the potential for the automatic plate-feed operation to be stopped by planographic printing plates and interleaf sheets adhering to the bottom of the raised planographic printing plate and being integrally supplied with the raised planographic printing plate.
Japanese Patent Application Laid-Open (JP-A) No. 2-25845 discloses an interleaf sheet comprising synthetic pulp mixed paper to which heat pressing has been administered. By forming the interleaf sheet in this manner, peelability of the interleaf sheet with respect to the planographic printing plate is improved and damage to the applied film is prevented.
However, since synthetic pulp is itself expensive, the cost of materials for the interleaf sheet becomes high. Further, since it is necessary to manufacture the synthetic pulp by separating it from general paper, manufacturing costs for the interleaf sheets also become high.
If it were possible to determine that the image forming surfaces of the planographic printing plates have a predetermined strength strong enough to withstand damage when packaged without using interleaf sheets, then it would become unnecessary to use the interleaf sheets and the aforementioned drawbacks would be eliminated.
However, as stated previously, because no quantitative standards or indices for such strengths of image forming surfaces have been proposed, at present, planographic printing plates are generally stacked with interleaf sheets disposed between the planographic printing plates in order to more reliably prevent damage to the image forming surfaces of the planographic printing plates.
In view of the aforementioned facts, it is a first object of the present invention to obtain a method (hereinafter, xe2x80x9cthe methodxe2x80x9d) for measuring strength of an image forming surface of a planographic printing plate, with the method being for measuring quantitative standard of strength by which it can be determined that the image forming surface of the planographic printing plate will not sustain damage in a packaged state. It is a second object of the present invention to obtain: a method for measuring strength of an image forming surface of a planographic printing plate, with the method being for measuring quantitative standard of strength by which it can be determined that the image forming surface of the planographic printing plate will not sustain damage in a packaged state, even without using interleaf sheets; a planographic printing plate with which damage to an image forming surface thereof in a packaged state can be prevented by strength of the image forming surface being measured by the method for measuring the strength of an image forming surface of a planographic printing plate; and a structure for packaging the planographic printing plates.
The method of the present invention comprises the steps of: contacting, with an image forming surface to be measured, a member expected to contact the image forming surface of the planographic printing plate in a packaged state; sliding, relative to each other and in a direction along the image forming surface, the planographic printing plate including the image forming surface to be measured and the member expected to contact the image forming surface of the planographic printing plate, while a predetermined load is applied to the planographic printing plate and the member in a direction substantially orthogonal to the image forming surface; and thereafter observing the planographic printing plate for the presence of damage to the image forming surface that is measured, and using a maximum value of pressure that does not generate damage when applied to the image forming surface as the strength of the image forming surface of the planographic printing plate.
In the present invention, the image forming surface to be measured is contacted with the member (hereinafter, occasionally referred to as xe2x80x9cthe contact memberxe2x80x9d) expected to contact the image forming surface of the planographic printing plate in a packaged state. Further, a state is created that approximates a state in which the planographic printing plates are packaged (stacked) by applying a predetermined load to the planographic printing plate and the contact member in a direction substantially orthogonal to the image forming surface. In the packaged state, when the planographic printing plate including the image forming surface to be measured and the contact member are slid in a direction along the image forming surface, the potential for the image forming surface of the planographic printing plate to sustain damage becomes greater. In addition, whether the image forming surface of the planographic printing plate actually sustains damage depends on whether or not the pressure acting on the image forming surface exceeds a predetermined threshold. Therefore, a state in which there is a potential for the image forming surface to sustain damage is created by applying, in a direction substantially orthogonal to the image forming surface, a predetermined load (pressure) to the planographic printing plate and the contact member, and then sliding, relative to each other and in a direction along the image forming surface, the planographic printing plate including the image forming surface to be measured and the contact member.
Thereafter, in the observation step, the image forming surface of the planographic printing plate is observed for the presence of damage, and the maximum value of pressure that does not generate damage when applied to the image forming surface is used as the strength of the image forming surface of the planographic printing plate. That is, the maximum value of pressure that does not generate damage when applied to the image forming surface, even in a state in which there is the potential for the image forming surface to sustain damage, is used as strength of the image forming surface of the planographic printing plate. Moreover, the observation step can also be carried out before various processings for forming an image are administered to the planographic printing plate and directly after the sliding step. However, depending on, for example, the type of planographic printing plate and purpose, the observation step can be carried out after various treatments such as exposure and development have been completed.
In the method of the present invention, the image forming surface strength that becomes an index of whether or not the image forming surfaces will sustain damage when the planographic printing plates are actually packaged can be quantitatively measured. Moreover, because it also becomes possible to achieve an optimal packaging structure in accordance with the type of planographic printing plate on the basis of the measured image forming surface strength, damage to the image forming surface can reliably be prevented.
In the present invention, there are no particular limitations on the contact member, as long as the member is one that is expected to contact the image forming surface in a state in which the planographic printing plates are packaged. For example, in addition to interleaf sheets and protective cardboards (i.e., cardboards disposed between the planographic printing plates at every predetermined number of sheets thereof, or disposed at end surfaces in the stacking direction of the stacked sheaf, to prevent damage to or deformation of the planographic printing plates due to an external force or the like), internal or external packaging materials can be used. Therefore, the contact member is not limited to any of those described above. A planographic printing plate having the same structure as that of the planographic printing plate having the image forming surface to be measured may also be used as the contact member.
By specifying the contact member to be a planographic printing plate having the same structure as the planographic plate having the image forming surface to be measured, the method of the present invention is also specified, and the numerical value of the image forming surface strength is determined by a single standard (i.e., there are not several different values resulting from differences in measurement conditions).
In the method of the present invention, a state is created during measurement that approximates a state in which only the planographic printing plates are stacked without the use of interleaf sheets. Therefore, the image forming surface strength that becomes an index of whether or not the image forming surface will sustain damage can be quantitatively measured. In other words, when the planographic printing plates are stacked and packaged, whether or not damage to the image forming surface can be prevented, even without the use of interleaf sheets, can be specifically determined on the basis of the value of the image forming surface strength. For example, when the planographic printing plates are handled in a state in which they are stacked and packaged, damage to the image forming surfaces thereof can be reliably prevented even without the use of interleaf sheets, as long as the image forming surface strength measured by the method of the present invention is a constant value or higher. Moreover, since the interleaf sheets are not used, the planographic printing plates can be packaged at a low cost. Further, the interleaf sheets are not used when the planographic printing plates are fed by the automatic plate-making mechanism. Therefore, such drawbacks as the interleaf sheets adhering to the non-image forming surfaces of the planographic printing plates and being supplied in a state in which the interleaf sheets and the planographic printing plates have become integrated (non-removal of the interleaf sheets), whereby the plate-feed operation is halted, do not occur. Moreover, since interleaf sheets are not used, the amount of waste after the packaging structure is opened is reduced.
When the value of the image forming surface strength measured by the method of the present invention does not reach the constant value and interleaf sheets are not used, i.e., in cases where there is the potential for the image forming surface to sustain damage, it is still possible to reduce the damage to the image forming surface to the extent that problems are not caused in actual use. Depending on whether the numerical value of the image forming surface strength is large or small, damage to the planographic printing plates can be reduced by, for example, handling the planographic printing plates with care.
Because a planographic printing plate having the same structure as the planographic plate having the image forming surface to be measured is used as the contact member, there is no need to prepare another member as the contact member. For this reason, measurement of the image forming surface strength can be conducted easily.
There are two types of the planographic printing plate: one having an image forming surface on one side only and one having an image forming surface on each side. In a case in which planographic printing plates having an image forming surface on each side are contacted in the contacting step, respective image forming surfaces come into contact with each other. In contrast, planographic printing plates having an image forming surface on one side only are customarily stacked so that each of the image forming surfaces faces one direction. Therefore, it is acceptable if the image forming surface of the planographic printing plate and the non-image forming surface of the same are disposed so as to contact one another.
The planographic printing plate used as the contact member is specifically selected for the purpose of measuring the image forming surface strength in a simple manner. The member to be used in the actual packaging structure of the planographic printing plates is not limited to a planographic printing plate. Namely, in the state in which the planographic printing plates are packaged, the contact member can be, for example, not only a planographic printing plate but an interleaf sheet, protective cardboard, or internal or external packaging material.
When the strength of the image forming surface is no less than 490 Pa, damage to the image forming surface can be reliably prevented by using protective materials for the planographic printing plates, such as interleaf sheets.
Even when the protective materials for the planographic printing plates are not used, damage to the image forming surface can be reduced by handling the planographic printing plates more carefully, since a constant image forming surface strength is ensured.
It is also acceptable to dispose a protective material (such as an interleaf sheet) between each of the planographic printing plates, which have an image forming surface strength of no less than 490 Pa, to form a stacked sheaf. As a result, damage to the image forming surfaces of the planographic printing plates is prevented.
When the strength of the image forming surface is no less than 980 Pa, damage to the image forming surface can be reliably prevented even when the planographic printing plates are handled, for example, in a stacked and packaged state without the use of interleaf sheets.
When the planographic printing plates are actually packaged, sometimes protective materials (interleaf sheets or protective cardboards) for protecting the planographic printing plates are used. Generally, when the protective material contacts the image forming surface of the planographic printing plate, it becomes more difficult for the image forming surface to sustain damage in comparison to when the planographic printing plates contact one another directly (i.e., when non-image forming surfaces or image forming surfaces are disposed adjacent to image forming surfaces). Accordingly, when the strength of the image forming surface is no less than 980 Pa, damage to the image forming surface can be reliably prevented when only the planographic printing plates are stacked. However, even when the protective materials are used in stacking the planographic printing plates, a sufficient value can be ensured as the image forming surface strength to prevent damage to the image forming surfaces.
The planographic printing plates can be fed by an automatic plate-feed mechanism.
When the planographic printing plates are fed by the automatic plate-feed mechanism, it is possible that the interleaf sheets become unnecessary for preventing the image forming surfaces from sustaining damage. For example, such drawbacks as the interleaf sheets adhering to the non-image forming surfaces of the planographic printing plates and being supplied in a state in which the interleaf sheets and the planographic printing plates have become integrated, whereby the plate-feed operation is halted, do not occur.
The planographic printing plates xe2x80x9cfed by the automatic plate-feed mechanismxe2x80x9d described above include all planographic printing plates manufactured with the assumption that the planographic printing plates will be fed by an automatic plate-feed mechanism, and also all planographic printing plates for which there exists the potential to be supplied by an automatic plate-feed mechanism. Thus, during actual conditions of use, it does not matter whether the planographic printing plates are fed by an automatic plate-feed mechanism or manually.
The image forming surface of the planographic printing plate can comprise a recording layer whose solubility in developer is altered by irradiation with laser light.
Generally, a planographic printing plate having the image forming surface comprising a recording layer is susceptible to damage. However, in the present invention, since the image forming surface strength is no less than 490 Pa (preferably no less than 980 Pa), it is possible to prevent damage to the image forming surfaces without the use of interleaf sheets.
It is possible to record an image directly on the image forming surface of a planographic printing plate having such a recording layer by irradiation with laser light.
The planographic printing plates whose image forming surface strength is no less than 490 (preferably no less than 980) can be stacked to form a stacked sheaf, and the stacked sheaf can be packaged by a packaging member to thereby form a packaging structure for the planographic printing plates. Therefore, it becomes possible to prevent the image forming surfaces from sustaining damage without the use of interleaf sheets. Since interleaf sheets become unnecessary, the packaging structure for the planographic printing plates can be achieved inexpensively. Further, when the planographic printing plates are fed by the automatic plate-feed mechanism, since interleaf sheets are not used, such drawbacks as the interleaf sheets adhering to the non-image forming surfaces of the planographic printing plates and being supplied in a state in which the interleaf sheets and the planographic printing plates have become integrated, whereby the plate-feed operation is halted, do not occur. Moreover, since labor to remove the interleaf sheets also becomes unnecessary, operation efficiency is improved. In addition, since interleaf sheets are not used, the amount of waste after the packaging structure (the packaging member) is opened is reduced.
Specifically, when the stacked sheaf is formed by the planographic plates without using interleaf sheets, direct contact of the planographic printing plates may be established: (1) between respective image forming surfaces; (2) between image forming surfaces and non-image forming surfaces; or (3) between respective non-image forming surfaces. If planographic printing plates having an image forming surface on both sides are used, contacts are always established between image forming surfaces. If planographic printing plates having an image forming surface on one side only are used, contacts are alternately established between image forming surfaces and between non-image forming surfaces, when the printing plates are stacked with each image forming surface alternately facing in opposite directions. Generally, if planographic printing plates having an image forming surface on one side only are used, the printing plates are stacked with every image forming surfaces facing in one direction, so that contacts are established between the image forming surfaces and the non-image forming surfaces.